This invention pertains to a method and apparatus for cutting and retrieving submerged trees.
Forested valleys can become flooded by natural causes or by hydroelectric damming. This results in free standing trees becoming submerged. It is desirable to harvest these submerged trees for commercial use.
It is known to provide a vessel, such as a barge, for floating on the surface of the water, with a mounted boom capable of extending under the water surface to cut underwater trees or stumps. Such apparatuses are described, for example, in U.S. Pat. No. 5,613,537, issued to Gassiott and U.S. Pat. No. 5,655,584, issued to Glawson. U.S. Pat. No. 6,024,145, issued to Ackles describes an articulated boom mounted to a free floating platform for use in manipulating objects under water. Such apparatuses are, however, limited to water depths equal to or less than the length of the boom. Such apparatuses are not effective in harvesting trees submerged in great depths of water.
U.S. Pat. No. 3,719,116, issued to Burton et al. describes an xe2x80x9cUnderwater Saw for Tree and Stump Removalxe2x80x9d. An underwater component is connected to a surface vessel by a flexible umbilical connection. The underwater component has hydraulically-operated propellers for depth control and has a pair of front-mounted horizontal saw blades to cut submerged trees and stumps. This apparatus does not contemplate any means to retrieve the cut trees other than allowing them to float to the surface. However, some submerged trees become waterlogged, and thus will not rise to the water surface on their own.
U.S. Pat. No. 5,868,182, issued to Burton describes a xe2x80x9cSubmersible Logging Devicexe2x80x9d having a frame with two traction wheels for moving along the bottom surface of the body of water. The frame has a sawing apparatus in an intermediate portion of the frame for cutting adjacent free standing timber. The frame also includes a xe2x80x9cdogging devicexe2x80x9d for fastening a line to the cut tree for retrieval thereof to the surface.
It is apparent that prior art underwater logging systems suffer from serious shortcomings, particularly in the case of trees submerged at great depths. The need has therefore arisen for a method and apparatus for cutting and retrieving submerged trees which employs air bags deployed and inflated by a remotely operated vehicle for raising cut trees to the water surface.
This invention provides an apparatus that allows for the harvesting of submerged trees at increased water depths. The apparatus can cut submerged trees and retrieve the trees to the surface of the water. The apparatus includes a control unit positionable on a surface vessel, such as a barge, and an underwater vessel, such as a ROV, remotely controllable from the control unit. The control unit and underwater vessel may be operatively connected with an umbilical. The underwater vessel preferably includes a propulsion system for navigating the vessel under water, a grapple for releasably engaging one of the trees, a plurality of buoyant members sequentially ejectable from the underwater vessel, each of the members being attachable to one of the trees, and a saw for cutting the trees.
In one embodiment of the invention each of the buoyant members may comprise a cartridge having a gas inlet, a gas outlet and a gas passageway extending between the inlet and outlet; an inflatable bag coupled to the cartridge for receiving gas discharged from the gas outlet, the bag being adjustable between inflated and uninflated states; and a housing releasably connectable to the cartridge for containing the inflatable bag in the uninflated state. The housing includes a sealable chamber for containing a buoyant material. The buoyancy of the sealable chamber is adjustable to alter the buoyancy characteristics of the housing. Preferably the underwater vessel is xe2x80x9cbuoyancy neutralxe2x80x9d meaning that the ejection of buoyant members from the vessel does not substantially affect the buoyancy characteristics of the vessel. The housing may also comprise a filament for tethering the housing to the bag.
The underwater vessel may further include a magazine located within the underwater vessel for holding a plurality of the buoyant members. Each of the buoyant members is movable between a storage position in the magazine and a deployed position proximate one of the trees. An ejection track is located at a front end of the underwater vessel above the saw for transferring each of the buoyant members from the storage position to the deployed position. In one embodiment, the magazine may comprise a track; a chain drive moveable around the track; and a plurality of magazine rails extending upwardly from the chain drive at spaced intervals. An indexer controllable from the control unit is provided for advancing the chain drive around the track in predetermined increments as each buoyant member is ejected. Each of the cartridges has a slot formed in a base portion thereof for receiving one of the magazine rails. The ejection track may include a shuttle moveable between a loading position proximate the magazine and a deployed position proximate one of the trees, the shuttle having a shuttle rail alignable with one of the magazine rails to enable sliding movement of one of the cartridges from the magazine on to the shuttle in the loading position. The shuttle rail has an aperture extending therethrough which is alignable with the gas inlet of a cartridge loaded on the shuttle.
The apparatus further includes a cartridge advancement assembly on the underwater vessel for actuating sliding movement of a cartridge from the magazine on to the shuttle when the shuttle is in the loading position. A shuttle actuator is also provided for actuating movement of the shuttle between the loading and deployed positions. A housing ejector is disposed proximate to the ejection track for ejecting the housing from the cartridge loaded on the shuttle to enable inflation of the inflatable bag. Each inflatable bag is inflated on the underwater vessel from a gas supply.
The grapple is disposed below the saw at a front end of the underwater vessel, the grapple comprising a central grapple frame and a pair of grapple arms each pivotably coupled to the frame, wherein the grapple arms are movable between an open position for receiving one of the trees therebetween and a closed position embracing the tree. An extraction ram is provided for advancing the grapple frame forwardly between a retracted position and an extended position. The extraction ram may be actuated, for example, when the saw becomes stuck in a tree during the cutting operation.
The invention also relates to a method of cutting and retrieving a tree submerged underneath the surface of a water body comprising the steps of:
(a) providing a remotely controlled underwater vessel, wherein the vessel carries at least one inflatable bag;
(b) releasably engaging the underwater vessel to the tree;
(c) fastening the inflatable bag to the tree;
(d) inflating the inflatable bag;
(e) cutting the tree at a location below the inflatable bag; and
(f) disengaging the underwater vessel from the tree to allow the tree and the inflatable bag to rise together to the surface of the water body for retrieval.
Preferably the underwater vessel is operatively coupled to a surface vessel located on the surface of the body of water and the step of inflating the inflatable bag comprises delivering gas from a gas supply on the surface vessel to the underwater vessel.
The various steps of the method are remotely controlled by an operator on the surface vessel. In order to facilitate such remote control, the method includes the steps of transmitting position signals from the underwater vessel to the surface vessel through the umbilical indicative of the position of the underwater vessel relative to a tree; and processing the signals on the surface vessel to generate a visual display viewable by the operator showing the position of the underwater vessel.
Additional features and advantages of the invention are described in detail below.